The invention relates to arrangement in which an electronic sensor controls the operation of an electric windshield wiper motor in dependence upon the detection of electrically conductive precipitation. The sensor is comprised basically of two spaced, naked electrical conductors arranged in front of their respective mounting means so as to be freely exposed to electrically conductive precipitation. These conductors serve as sensing elements operative, as part of an electric control circuit, for generating a control signal in response to a change in the electrical resistance between them.
A sensor of this general type is disclosed in Federal Republic of Germany published patent application DT-OS No. 2,255,264. In that construction, the sensor elements are comprised of a plurality of stationary metal rods arranged in a fan-like manner. The distance and accordingly the electrical resistance between the sensor elements increases along the length of the measuring path. This sensor does in fact perform its intended function; however its sensitivity, especially in the case of changing weather conditions, is not always sufficient. It has been determined that the principal cause of the unsatisfactory operation of this known construction is that extremely small droplets became caught in the measuring path in the narrow spaces between adjoining sensor elements and, in some circumstances, cause the sensor to generate for a considerable length of time a signal indicative of a weather condition not actually in existence. It would be possible to overcome this difficulty by increasing the interelectrode spacing; however, that would in turn so greatly reduce the sensitivity of the sensor as to practically destroy its utility.